flowable/flowable-engine · error · FlowableIllegalArgumentException

Deserialized value is not an array of ID's:

Error message

Deserialized value is not an array of ID's: 

What it means

When reading a JPA entity list variable back, deserializeIds Java-deserializes the stored bytes and requires the result to be a String[]. If the deserialized object is anything else, FlowableIllegalArgumentException is thrown.

Solutions

1. Inspect the stored BYTE value in the variable table and delete/repair the corrupted variable
2. Re-set the variable with a valid list of JPA entities to rewrite correct bytes
3. Check Flowable upgrade notes for variable serialization format changes and migrate data
4. Ensure no other code writes to the same variable byte array

Example fix

// before
// legacy variable row with non-String[] bytes
SELECT BYTES_ FROM ACT_RU_VARIABLE WHERE NAME_='customers'; -- inspect
// after
runtimeService.setVariable(executionId, "customers", validEntityList); // rewrites bytes

// inspect persisted bytes before reading the variable
byte[] bytes = readVariableBytesFromDb("customers");
boolean looksValid = bytes != null && bytes.length > 0;

try { Object v = runtimeService.getVariable(executionId, "customers"); } catch (FlowableIllegalArgumentException e) { if (e.getMessage().startsWith("Deserialized value is not an array of ID's")) { runtimeService.setVariable(executionId, "customers", null); } else throw e; }

When it happens

Trigger: getValue → ids → deserializeIds encountering stored bytes that decode to a non-String[] object: bytes written by an older Flowable version with a different format, manual corruption, or bytes written for a different variable type.

Common situations: Upgrading Flowable where the persisted variable byte format changed; manually editing variable byte values in DB; reusing a variable name across incompatible value types.

Related errors

• Unexpected exception when deserializing JPA id's
• Cannot flush EntityManager, an active transaction is…
• Cannot set JPA variable:
• Could not deserialize event to json
• Could not deserialize event to xml

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/8b0b8608cb9e3b77. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-variable-service/src/main/java/org/flowable/variable/service/impl/types/JPAEntityListVariableType.java:163

            String[] toStore = ids.toArray(new String[] {});
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            ObjectOutputStream out = new ObjectOutputStream(baos);

            out.writeObject(toStore);
            return baos.toByteArray();
        } catch (IOException ioe) {
            throw new FlowableException("Unexpected exception when serializing JPA id's", ioe);
        }
    }

    protected String[] deserializeIds(byte[] bytes) {
        try {
            ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
            ObjectInputStream in = new ObjectInputStream(bais);

            Object read = in.readObject();
            if (!(read instanceof String[])) {
                throw new FlowableIllegalArgumentException("Deserialized value is not an array of ID's: " + read);
            }

            return (String[]) read;
        } catch (IOException | ClassNotFoundException ioe) {
            throw new FlowableException("Unexpected exception when deserializing JPA id's", ioe);
        }
    }

}

View on GitHub (pinned to d6d39ce1c6)